It is known to apply window safety film (hereinafter referred to as “window film”) to the inside face of window and door panes to prevent glass shattering. Such window film consists of a layer or layers of thin polyester adhesive film, which is applied to the inside surface of the glass (or transparent plastics sheet) to improve impact resistance, and also to hold loose shards of glass together when the glass is broken by an impact.
Such window films will reduce bomb blast injuries, since the film holds the loose shards together and the whole window pane will drop to the ground as one piece rather than hundreds of cutting shards. Similarly, such films are extensively used in schools and hospitals to resist falling body impact, eg where persons trip and fall against non safety-rated glass. The glass shatters, but it does not disintegrate into multiple shards, because the window film holds the shards together.
Thicker and stronger films are used to improve smash and grab resistance of retail shop windows. However, it is possible to gain entry by using a lever bar to prise the glass and film away from the edge of the frame, thus creating a hole to allow entry therethrough, eg smash and grab or forced entry.
When window film is fitted to the inside face of the glass of a window or door, a gap is usually left around the edge of the pane (normally referred to as a “daylight” gap) where the film is trimmed against the frame. This means that the glass and window film can drop out of the window or door frame if enough force is applied. After bomb blasts it is common to see complete glass sheets with film lying inside a building.
It is known to apply the film to the pane so that it overlaps the surrounding frame and to use a beading or profile to clamp the overlapping film to the surrounding frame. Although this does increase the security of the pane against impact considerably, there is a tendency for the film to stretch and tear along the edge of the profile during an impact. Furthermore, where the profile has a gasket engaging the film on the pane, there is also a tendency for the gasket to be pulled out by the film as it stretches during an impact
This problem is overcome by GB 2 327 700 B, which discloses a clamping profile comprising a first elongate side portion attachable by fixing means (eg screws) therethrough to the surrounding frame to clamp the overlapping film, and a second elongate side portion having a gasket protruding therefrom for cushioning impact movement of the pane and film. The first and second elongate side portions are substantially at right angles to each other and are connected by an elongate curved portion of the profile to minimise the risk of tearing of the film during an impact on the pane. The outer surface of the curved portion of the profile has a radius of curvature from 4 mm to 15 mm.
Although this clamping profile has proved successful in use, it is costly to manufacture and time consuming, and hence costly, to install. Furthermore, the window film must be wrapped around the frame, which also adds to the cost of installation.